This invention relates to the monitoring or measuring of the water cut or percentage of water present in produced fluids from a well borehole. More particularly, the invention relates to the use of microwave energy to measure the dielectric properties of multiphase fluids containing oil, water, gas and possibly entrained solids in a producing well, and the use of such measured dielectric properties to determine the water cut of the produced fluid directly.
A prior art co-assigned patent (U.S. Pat. No. 4,947,128) discloses a device and method for using microwave energy to measure the water cut of a petroleum stream based on the relative phase and the intensity of reflected and transmitted microwave energy impinging upon the petroleum stream. In this co-variance water cut monitoring scheme, however, for simplification of analysis certain assumptions are made. One critical assumption, used in the mini-computer program in the device, is that the continuous phase (i.e. oil continuous or water continuous) of the multiphase fluid flow is known. A priori knowledge of this parameter is not always possible and, even if initially known accurately, can change during the time period of the measurements themselves. Moreover it has been determined that other unknown variables can affect this measurement process such as temperature changes, changes in water salinity and changes in the type and quantity of solid impurities in the monitored production fluid stream.